Thermal recovery methods such as Steam Assisted Gravity Drainage (“SAGD”), Cyclic Steam Stimulation (CSS), Steamflooding, and In-Situ Combustion (ISC) have become some of the most widely used enhanced hydrocarbon recovery methods to extract hydrocarbons from subterranean hydrocarbon-containing formations.
Generally, the thermal processes use steam, which is generated at the surface and pumped into the formation, or heat is generated in-situ by various methods including electrical heating or in-situ combustion, to increase the hydrocarbon's fluidity and allow it to be collected and produced to surface.
The voidage created by removal of the collected hydrocarbon is generally occupied by steam and/or steam condensate and/or heated vapours. It is commonly referred to as a steam ‘zone’, or ‘chamber’ chest. It is an inherent aspect of these thermal chests, having a higher temperature than the surrounding formation(s), that they lose thermal energy with a consequent drop in pressure. There may also occur leak-off of the fluids through ‘thief zones’ which also depletes the pressure of the steam chest.
Maintaining an appropriate pressure is generally accomplished by injecting a combination of fluids and/or steam, and in some processes such as SAGD by gradually substituting the steam with a non-condensable gas (NCG), that is a gas which does not readily mix or be miscible with the liquids and will not appreciably condense into a liquid at reservoir operating conditions.
It is economically disadvantageous and/or in most cases impossible to develop an entire field simultaneously due to labour, capital, surface access and logistical constraints. Accordingly, fields are developed as a series of ‘stages’, ‘phases, ‘regions’ or ‘areas’ to maintain a balance of production and injection fluids between the field sites, and the appropriately sized processing plant and/or fluid handling system. It is economically, environmentally and socially desirable to be able to move surface equipment from exploited areas to non-exploited areas as quickly as possible, so as to allow for the injection and production equipment and manpower to be redirected to more profitable, partially exploited areas and/or open up new areas to be exploited, while at the same time allow surface reclamation to commence at the surface of regions that have already been exploited.
Different areas/regions within an overall recovery project are thus typically at different stages of development. When thermal recovery processes enter the mature stage and steam/thermal energy injection is reduced in an older, more exploited area, that area's pressure will decline, creating a flow potential for steam/fluids from adjacent areas under active exploitation, due to the hydraulic connectivity inherent in the reservoirs subject to thermal exploitation. This has the very undesirable consequence of accordingly needing to increase injection of fluids and/or thermal energy in the area being actively exploited above what otherwise would be needed for its specific exploitation.
In the recent Cenovus amendment application to the Alberta Energy Regulator (Application to amend approval 8623, Apr. 9, 2013; Application to amend approval 8623 May 4, 2010) for the Foster Creek thermal project which uses SAGD to exploit the bitumen from the McMurray Formation in the Athabasca Oil Sands region of Alberta, a ‘Wind Down’ (ramp-down of steam injection) process is described as a phased approach to allocate steam injection more effectively to other less exploited areas. It is disclosed that such is intended to be accomplishing by supplanting the steam with non-condensable gas in a stepped fashion, by continuing to inject NCGs in depleted regions to maintain pressures to avoid issues with artificial lift constraints and influx of water.
Numerous improvements on the general technique for recovering bitumen from underground formations have been developed.
For example US Pub. 2013/0062058 entitled “In Situ Combustion following SAGD” teaches a method for recovering petroleum from a formation. The formation is caused to be intersected by a well pair consisting of a horizontal production well and a horizontal injection well, and wherein said formation comprises at least one steam chamber developed by a steam-assisted process, said method comprising: providing an oxidizing agent near the top of said formation; initiating in situ combustion (ISC); and recovering petroleum from said at least one production well.
US Pub. 2012/0067512 entitled “Radio frequency enhanced steam assisted gravity drainage method for recovery of hydrocarbons” teaches a method for heating a hydrocarbon formation. A radio frequency applicator is positioned to provide radiation within the hydrocarbon formation. A first signal sufficient to heat the hydrocarbon formation through electric current is applied to the applicator. A second or alternate frequency signal is then applied to the applicator that is sufficient to pass through the desiccated zone and heat the hydrocarbon formation through electric or magnetic fields. A method for efficiently creating electricity and steam for heating a hydrocarbon formation is also disclosed. An electric generator, steam generator, and a regenerator containing water are provided. The electric generator is run. The heat created from running the electric generator is fed into the regenerator causing the water to be preheated. The preheated water is then fed into the steam generator. The RF energy from power lines or from an on site electric generator and steam that is harvested from the generator or provided separately are supplied to a reservoir as a process to recover hydrocarbons.
U.S. Pat. No. 4,508,168 entitled “RF Applicator for in situ heating” teaches a coaxially fed applicator for in situ RF heating of subsurface bodies with a coaxial choke structure for reducing outer conductor RF currents adjacent the radiator. The outer conductor of the coaxial transmission line supplying RF energy to the radiator terminates in a coaxial structure comprising a section of coaxial line extending toward the RF radiator from the termination for a distance approaching a quarter wavelength at the RF frequency and a coaxial stub extending back along the coaxial line outer conductor from the termination for a distance less than a quarter wavelength at said frequency. The central conductor of the coaxial transmission line is connected to an enlarged coaxial structure approximately a quarter of a wavelength long in a region beyond the end of the outer conductor coaxial choking structure.
US Pub. 2012/0061080 entitled “Inline RF heating for SAGD Operations” provides a method for accelerating start-up for SAGD-type operation by providing radio frequency heating devices inside the lateral wells that can re-heat the injected steam after losing heat energy during the initial injection. The method also extends the lateral wells such that the drilling of vertical wells can be reduced to save capital expenses.
US Pub. 2013/00199774 entitled “Heavy oil production with EM preheat and gas injection” teaches an enhanced oil recovery technique that combines gas injection with EM radiation to heat and mobilize heavy oil at least until fluid communication is achieved. This invention relates to methods of enhanced hydrocarbon recovery that combines gas drive mechanisms with RF mobilization of hydrocarbon deposits.
US Pub. 2013/0153210 entitled “In Situ RF heating of stacked pay zones” teaches a method of heating stacked pay zones in a hydrocarbon formation by radio frequency electromagnetic waves is provided. In particular, radio frequency antenna array having multiple antenna elements are provided inside a hydrocarbon formation that has steam-impermeable structure. The antenna elements are so positioned and configured that the hydrocarbons in the place where conventional thermal methods cannot be used to heat due to the steam-impermeable structure can now be heated by radio frequency electromagnetic waves. The invention relates to the production of heavy oils and bitumens from stacked pay zones using radio frequency radiation (RF) to heat and mobilize the oil.
US Pub. 2012/0318498 entitled “Electromagnetic Heat Treatment Providing Enhanced Oil Recovery” teaches a method for using RF energy to facilitate the production of oil from formations separated from the RF energy source by a rock stratum comprises operating an antenna to transmit RF energy into a hydrocarbon formation, the hydrocarbon formation comprised of a first hydrocarbon portion above and adjacent to the antenna, a second hydrocarbon portion above the first hydrocarbon portion, and a rock stratum between the first hydrocarbon portion and the second hydrocarbon portion. The operation of the antenna heats water in the hydrocarbon formation to produce steam in the hydrocarbon formation, and the steam heats hydrocarbons in the hydrocarbon formation and fractures the rock stratum to produce fissures in the rock stratum. The heated hydrocarbons in the second hydrocarbon portion flows into the first hydrocarbon portion through the fissures in the rock stratum.
US Pub. 2011/0011582 entitled “In situ combustion with multiple staged producers” teaches methods and apparatus relating to in situ combustion recovery. Configurations of the injection and production wells facilitate the in situ combustion. Utilizing wet combustion for some embodiments promotes heat displacement for hydrocarbon recovery with procedures in which one or more of the production and injection wells are configured with lengths deviated from vertical. In some embodiments for either dry or wet combustion, at least the production wells define intake lengths deviated from vertical and that are disposed at staged levels within a formation. Each of the production wells during the in situ combustion allow for recovery of hydrocarbons through gravity drainage. Vertical separation between the intake lengths of the production wells enables differentiated and efficient removal of combustion gases and the hydrocarbons.
U.S. Pat. No. 8,353,342 entitled “Hydrocarbon Production Process” teaches methods and apparatus relating to producing hydrocarbons. Injecting a fluid mixture of steam and carbon dioxide into a hydrocarbon bearing formation facilitates recovery of the hydrocarbons. Further, limiting amounts of non-condensable gases in the mixture may promote dissolving of the carbon dioxide into the hydrocarbons upon contact of the mixture with the hydrocarbons.
US Pub. 2012/0175110 entitled “In situ combustion in gas over bitumen formations” provides methods for natural gas and oil recovery, which include the use of air injection and in situ combustion in natural gas reservoirs to facilitate production of natural gas and heavy oil in gas over bitumen formations.
US Pub. 2008/0264635 entitled “Hydrocarbon recovery facilitated by in situ combustion utilizing horizontal well pairs” teaches hydrocarbon recovery processes that may be utilized in heavy oil reservoirs. Horizontal hydrocarbon production wells may be provided below horizontal oxidizing gas injection wells, with distant combustion gas production wells offset from the injection well by a distance that is greater than the hydrocarbon production well offset distance. Oxidizing gases injected into the reservoir through the injection well support in situ combustion, to mobilize hydrocarbons. The process may be adapted for use in a reservoir that has undergone depletion of petroleum in a precedential petroleum recovery process, such as a steam-assisted-gravity-drainage process, leaving a residual oil deposit in the reservoir as well as mobile zone chambers. Processes of the invention may be modulated so that a portion of the residual oil supports in situ combustion, while a larger portion of the residual oil is produced, by channeling combustion gases along the pre-existing mobile zones with the reservoir.
CA 2,493,306 entitled “In situ combustion following primary recovery processes utilizing horizontal well pairs in oil sands and heavy oil reservoirs” teaches processes for in situ combustion as a secondary recovery technique for recovery of oil by a combination of gravity drainage, hot gas drive and enhanced steam drive, particularly suited to oil sands or heavy oil reservoirs that have undergone a prior steam-based gravity controlled process.
US Pub. 2013/0284435 entitled “Satellite steam-assisted gravity drainage with oxygen (SAGDOX) system for remote recovery of hydrocarbons” teaches a SAGDOX satellite system for recovering hydrocarbons includes a central SAGDOX site, at least one SAGDOX satellite site, and a pipeline corridor for communication between the central SAGDOX site and the SAGDOX satellite site. The satellite system is designed to recover hydrocarbons using a SAGDOX process at the satellite site and transfer recovered hydrocarbons to the central site.
US Pub. 2013/0098603 entitled “Steam assisted gravity drainage processes with the addition of oxygen addition” teaches a process to recover hydrocarbons from a hydrocarbon reservoir, namely bitumen (API<10; in situ viscosity >100,000 c.p.), said process comprising: (a) establishing a horizontal production well in said reservoir; (b) separately injecting an oxygen-containing gas and steam into the hydrocarbon reservoir continuously to cause heated hydrocarbons and water to drain, by gravity, to the horizontal production well, the ratio of oxygen/steam injectant gases being controlled in the range from 0.05 to 1.00 (v/v); and (c) removing non-condensable combustion gases from at least one separate vent-gas well, which is established in the reservoir to avoid undesirable pressures in the reservoir.
US Pub. 2013/0098607 entitled “Steam flooding with oxygen injection, and cyclic steam stimulation with oxygen injection” teaches a process to recover heavy oil from a hydrocarbon reservoir, the process comprising injecting oxygen-containing gas and steam separately injected via separate wells into the reservoir to cause heated hydrocarbon fluids to flow more readily to a production well, wherein: i) the hydrocarbon is heavy oil (API from 10 to 20; with some initial gas injectivity); (ii) the ratio of oxygen/steam injectant gas is controlled in the range from 0.05 to 1.00 (v/v); and (iii) the process uses Cyclic Steam Stimulation or Steam Flooding techniques and well geometry, with extra well(s) or a segregated zone to inject oxygen gas wherein the oxygen contact zone within the reservoir is less than substantially 50 meters long.
US Pub. 2013/0175031 entitled “SAGDOX geometry” teaches a process to recover bitumen from a subterranean hydrocarbon reservoir comprising the following steps: a) injection of steam and oxygen separately into said bitumen reservoir and when mixed therein said mix being in the range of 5 to 50% O2; b) production of hot bitumen and water using a horizontal production well; and c) production/removal of non-condensable combustion gases to control reservoir pressure.
U.S. Pat. No. 4,524,826 entitled “Method of heating an oil shale formation” teaches a method of heating an oil shale formation to produce shale oil including radiating RF energy into the oil shale formation for a predetermined first time interval from a first borehole which penetrates said oil shale formation. Shale oil is produced when available during said first time interval from a second borehole penetrating said oil shale formation which is a predetermined distance from the first borehole. During a predetermined second time interval, RF energy is again radiated into the oil shale formation from the second borehole while shale oil is produced from the first borehole during the second time interval.
US Pub. 2009/0050318 entitled “Method and apparatus for in-situ radiofrequency assisted gravity drainage of oil (RAGD)” teaches a radiofrequency reactor for use in thermally recovering oil and related materials. The radiofrequency reactor includes a radiofrequency antenna configured to be positioned within a well, where the well is provided within an area in which crude oil exists in the ground. The radiofrequency antenna includes a cylindrically-shaped radiating element for radiating radiofrequency energy into the area in which crude oil exists. The cylindrically-shaped radiating element is configured to allow passage of fluids therethrough. The radiofrequency reactor also includes a radiofrequency generator electrically coupled to the radiofrequency antenna. The radiofrequency reactor is operable to control the radiofrequency energy generated.
US Pub. 2003/0155111 entitled “In situ thermal processing of a tar sands formation” teaches an in situ process for treating a tar sands formation. Heat from one or more heaters is provided to a part of the formation, which pyrolyzes at least some hydrocarbons within the part, which may be subsequently produced.
US Pub. 2013/0199777 entitled “Heating a hydrocarbon reservoir” teaches a system and method for heating a hydrocarbon reservoir, wherein the reservoir includes a reduced oil saturation zone in proximity to a heavy oil zone. The method includes injecting an oxidizing gas into the reduced oil saturation zone and combusting hydrocarbons included within the reduced oil saturation zone. The method also includes determining a level of heating within the heavy oil zone that is conductively heated by combustion of the hydrocarbons within the reduced oil saturation zone, and producing hydrocarbons from the heavy oil zone once a desired level of heating has occurred.
US Pub. 2013/0025858 entitled “Solvent and gas injection recovery process” teaches a process for the recovery of hydrocarbon such as bitumen/EHO from a hydrocarbon bearing formation in which are situated an upper injection well and a lower production well, the method comprising the steps: preheating an area around and between the wells by circulating hot solvent through the completed interval of each of the wells until sufficient hydraulic communication between both wells is achieved; injecting one of more hydrocarbon solvents into the upper injection well at or above critical temperature of the solvent or solvent mixture, thereby causing a mixture of hydrocarbon and solvent to flow by gravity drainage to the lower production well; and producing the hydrocarbon to the surface through the lower production well. A non-condensable gas may be injected into the solvent chamber created by the hydrocarbon solvent.
CA 1,164,335 entitled “In situ combustion of tar sands with injection of non-condensable gases” teaches an in-situ combustion recovery process whereby recovery of tar sands is improved by introducing into the tar sand formation a stream of relatively light hydrocarbon gas. The stream of light hydrocarbon gas may contain a small proportion of hydrocarbons condensable at temperature and pressure conditions of the tar sand formation. The improvement is applicable to both forward and reverse in-situ combustion processes.
US 2010/0282644 entitled “Systems and methods for low emission hydrocarbon recovery” teaches systems and methods for low emission (in-situ) heavy oil production, using a compound heat medium, comprising products of combustion of a fuel mixture with an oxidant and a moderator, mixed with steam generated from direct contact of hot combustion products with water, under pressure. The compound heat medium, comprising mainly CO2 and steam, is injected at pressure into a hydrocarbon reservoir, where steam condenses out of the compound heat medium releasing heat to the reservoir. The condensate is produced with the hydrocarbon as a hydrocarbon/water mixture or emulsion. Non-condensable gases, primarily CO2, from the compound heat medium may remain in the reservoir through void replacement and leakage to adjacent geological strata. Beneficially, any CO2 produced is recovered at pressure, for use in other processes, or for disposal by sequestration. Produced water is recovered and recycled as a moderator and steam generating medium.
As may be seen from the above prior art publications, prior art methods for maintaining pressure in the already exploited regions have consisted of injection of other (typically non-heated) gases (referred to in the art as “non condensable gases” or “NCGs”) which do not require heating, and are less expensive than steam to generate or acquire and inject. NCGs often employed for this purpose include nitrogen, carbon dioxide, methane, and air, all of which serve the main purpose of maintaining the pressure in the exploited region and thereby avoid leakage of (expensively heated) steam (which is injected into an unexploited region) into the exploited region.
Problematically, however, developing adjacent unexploited regions of a reservoir becomes difficult (or at least more expensive) if no readily-available or cheap source of NCG's is available to inject into an adjacent hydrocarbon-depleted region, and thus steam is needed to be continued to be injected into such “already exploited” (i.e. no longer producing) regions in order to exploit other adjacent regions. Such a scenario (i.e. where no cheap or readily-available source of NCG's is available at the location of the formation being developed, which is a not-uncommon occurrence) typically will render the ratio of injected steam to oil recovered (i.e. the Steam to Oil Recovery ratio or “SOR”) too high for profitable recovery, including, potentially the requirement for greater capital expenditures to acquire larger and higher capacity steam generation equipment to compensate for the leakage of steam back into regions which have been exploited and are relatively depleted of hydrocarbons.
Also problematic is the necessity, in order to exploit undeveloped regions of the formation, of maintaining injection of steam and/or NCGs on the surface above the exploited (non-producting) regions, which thereby impedes surface reclamation activities, including freeing-up manpower for reclamation activities, until such surface equipment can be removed from above such exploited areas, which is typically only after the adjoining region being exploited itself becomes depleted.
Accordingly, a real need exists in the thermal hydrocarbon-recovery industry for a method of maintaining pressure in the more exploited regions of a reservoir which lessens or eliminates the need for generation and/or injection of steam and/or NCGs into adjacent more exploited regions, to more economically recover bitumen from the less exploited regions, while facilitating greater surface reclamation.
Such a method, if developed and utilized, could further allow for re-development of existing partially-developed reservoirs which possess regions which have been already exploited or partially exploited, but which further possess unexploited regions which have not been developed due to the aforesaid problem of leakage of heated steam into adjacent exploited regions.
In addition, where a reservoir possesses bitumen-containing regions interspersed with adjacent, permeable regions containing little to no bitumen, and where no cheap supply of NCGs is readily available at the location of a reservoir to otherwise pressurize such non-bitumen producing regions, a real need exists for a method of developing the bitumen-containing regions of the reservoir where the non-bitumen containing regions would otherwise, without the benefit of this technology, operate as “thief” zones and prevent the steam injected in the bitumen-containing regions from condensing in such bitumen containing regions, so as to thereby allow the effective and/or economical production from such bitumen-containing regions of the reservoir.